Losing steps/position, again

[Doddy]

Interesting that "Modded" worked - that suggests your pulse width (somewhere in the motor tuning pages of Mach3 by memory) is less than 3uS. Try changing that to 5us for reliable operation.

EDIT: Silent?, Nonsense - you'll appreciate silent when you replace with a digital DSP controller.

[ngwagwa]

Interesting that "Modded" worked - that suggests your pulse width (somewhere in the motor tuning pages of Mach3 by memory) is less than 3uS. Try changing that to 5us for reliable operation.

They are all set at zero! Can I leave them for now and look at them when I go over to UUCNC?

[JAZZCNC]

Not a clue to be honest I would appreciate an explanation. After homing the machine appears to be going to the correct point when I zero all.

If that case you have been lucky and set MS to same as old setup (you can pick my lottery numbers)
Edit: No your probably not lucky, obviously it will go to the same point because the Home switch stops it and sets the zero. If you tell it to move say 20mm does it move 20mm.?

Ok well, it's not hard but it is important. I'll try to keep short n simple but it will still be long.!.

Your steppers will have a base count number of steps per revolution, often this number is 200 or 1.8deg per step. But this can be different depending on the motors but I'll work on that for this example because it's most common.

Now the drives offer a function that allows each step to be broken down into sub-steps or Micro steps (MS). The drive will offer a range of MS dividers ie: 2, 4, 8, 16, etc or sometimes you'll see them wrote as 400, 800, 1600, 3200 etc. They all mean the same thing and tell you how many times they are going to divide each step up or like in later example how many steps make up one Revolution of the stepper.

Now the controller needs to be told how many Steps(pulses) it must send out to move the machine 1 unit of measurement, So if set to metric how many Steps per MM.
This is determined by a calculation for which we need some information about the machine.

We need to know how far it moves for one turn of the motor shaft. Now linear movement can be done in many ways ie: ball screws, rack n pinion, belt-drive, etc but this doesn't matter all we need to know is how far it moves for 1 turn of the motor shaft.

The easiest way is to just turn the motor one Rev and measure how far it moved but this need to be measured very accurately. But we can also calculate it if we know some details about the machine. In this case, I'm going to work on using ball screws.

So using a 5mm Pitch ball screw and set the drives to 8 which is like saying 8 x 200 or 1600 MS we will get the following Step Per figure.
1600/5=320 Steps per MM

Now if the ball screws and motor are connected via a belt with a ratio then we need to factor that in as well. So lets say we have a 2:1 ratio then we get.
1600/5 =320/2=160 Steps per MM

This is the number you enter into Mach3 Steps Per setting so that the machine moves the correct distance.
The Steps Per setting is very important and not something that can be guessed or random numbers entered.

The speeds you'll get from the machine will be determined by the Steps Per value and the Frequency you have available. The pitch of the screws, motors and voltage etc all play a part here and are why a balanced setup works best. I'll leave that for another time!



Now the affects Micro stepping as on the Motors and the system as a whole gets a little deep so won't go too far into it. I'll just give the key advantages and downsides.

The main advantage to micro-stepping on the motors is they make them run smoother, you'll often see it mentioned it offers high resolution, which it does to some degree but it shouldn't really be relied upon. The largest effect is on the smoothness of the motors.

The down side is it lowers the motor torques and puts a higher strain on the device which is creating the pulses.

Now to you both of these are important because in the first place these motors don't have massive Torque and your also using the parallel port which is limited in frequency and on how fast it can pump out pulses.

So in your case, you'll be better using lower MS because it will allow a higher number of pulses which translates to potential higher feed rates, but you still want some motor smoothing, so don't drop right down to the lowest setting as it can make the motors run very rough.

4 x (800) is a good number but some times you may need 2 x (400) to give you the speed because of the in-balance as mentioned above and lower frequency etc.

Some times a certain MS setting won't suit the motor because resonance in the machine when working can affect how the motor runs, so in cases like these, esp with a parallel port and cheap drives, you have to move the MS range up or down to find a sweet spot the motor likes. This happens a lot on analog and shitty drives.
Newer Digital drives are much much better at handling resonance and along with faster motion controllers like the AXBB completely transform a machine, even with old lower torque motors.


I hope this hasn't blown your mind.
Simply put if you don't set the Steps Per correctly it will never be accurate and if you set the MS too high you'll stress the parallel port and run slow.!!

[Doddy]

They are all set at zero! Can I leave them for now and look at them when I go over to UUCNC?

Your call.

I'll tell you the behaviour if the pulse width is too low... You lose steps.

[ngwagwa]

Your call.

I'll tell you the behaviour if the pulse width is too low... You lose steps.

Right I will change them when I go in tomorrow.

[ngwagwa]

If that case you have been lucky and set MS to same as old setup (you can pick my lottery numbers)
Edit: No your probably not lucky, obviously it will go to the same point because the Home switch stops it and sets the zero. If you tell it to move say 20mm does it move 20mm.?

Sorry I didn't explain that too well, after homing the machine it went to the work datum ie G55 0,0,0 (machine position X-355, Y-130 and Z-45}. I was assuing that as none of the Mach3 settings had changed all would be good.

Thanks for the explnation and I get the general idea - the "steps per" on the current setup is <Steps0>31.50619418</Steps0> guessing maybe imperial pitch lead screws.

I am hoping to have all the parts for the retro-fit by the end of next week (the toroidal transformer may be later as they say This was only ordered today! It takes 2/3 days for us to wind the order.) Anyway I can hopefully forget any serial port imitations when the new motion controller is installed. Changing the wiring on the Y and Z steppers is going to be a bitch if they are wired the same as the X axis.

Meanwhile I will set a job running tomorrow and start working out the layout of the new parts and how to get them in the control box.

[JAZZCNC]

Thanks for the explnation and I get the general idea - the "steps per" on the current setup is <Steps0>31.50619418</Steps0> guessing maybe imperial pitch lead screws.

No that will be metric. If it was imperial it would be much higher number.

[ngwagwa]

Apparently I havn't got as much room in the cabinet as I thought.

[Doddy]

Apparently I havn't got as much room in the cabinet as I thought.

QFT: That single statement is what we've all felt like at some time. Today I've been stacking BoBs on top of BoBs, and Relay boards on top of PSUs... and the cabinet always looked too big on paper.

It's not big or clever, but there's always the third dimension.

[ngwagwa]

It's not big or clever, but there's always the third dimension.

That's why I modelled it solids.